<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .f {
            width: 500px;
            border-top: 3px solid cadetblue;
        }

        .s1 {
            width: 200px;
            height: 200px;
            background-color: orangered;
            float: left;
        }

        .s2 {

            float: left;
        }

        .other {
            width: 300px;
            height: 300px;
            background-color: yellowgreen;
            clear: both;
        }
    </style>
</head>


<body>
    <div class="f">
        <div class="s1"></div>
        <div class="s2"></div>
    </div>

</body>

</html>